1. Field of the Invention
This invention pertains generally to fluidic nanotube devices, and more particularly, to functionalized nanochannels providing modifiable channel geometry and ionic environment and devices fabricated therefrom.
2. Description of Related Art
The detection and analysis of interactions between biological molecules is a significant area of research in the healthcare and biotechnology fields. Many molecular detection, analysis and separation techniques have been developed and validated in recent years. For most processes, efficiency is a result of a trade-off between sensitivity, specificity, ease of operation, cost, speed and avoidance of false positives. Typical biological sensing techniques require a series of preparation steps, a number of reagents and schemes to separate components, a relatively large sample size and complex data analysis.
Miniaturization and mechanization of biological sensing techniques can lower sample sizes, reduce the time and expense of the process and increase diagnostic sensitivity. Emerging micro- and nano-technologies can decrease the size, weight and cost of sensors and sensor arrays by orders of magnitude, and increase their spatial and temporal resolution and accuracy. Novel functional materials such as quantum dots, photonic crystals, nanowires, carbon nanotubes, porous membranes, porous silicon and sol-gel matrices incorporating biomolecules have been used as sensing elements with various possible detection mechanisms.
Hollow inorganic nanotubes are of particular interest due to their potential applications in bioanalysis and catalysis. For example, silica nanotubes are of special interest because of their hydrophilic nature, easy colloidal suspension formation, and surface functionalization accessibility for both inner and outer walls. Such modified silica nanotubes and nanotube membrane have shown potential applications for bioseparation and biocatalysis.
In addition, one-dimensional nanostructures (nanotubes and nanowires) have also made miniaturized chemical and biological sensing elements possible. The ultrahigh surface to volume ratios of these structures make their electrical properties extremely sensitive to surface-adsorbed species, as has been shown with carbon nanotubes, functionalized silicon nanowires and metal nanowires
Chemical and biological nanosensors are advantageous because of their potential for detecting very low concentrations of biomolecules or pollutants on platforms small enough to be used in vivo or on a microchip. For example, a room temperature photochemical NO2 sensor has been demonstrated based on individual single-crystalline oxide nanowires and nanoribbons.
Chemical/sensing systems have also been developed using silica tubular membranes creating a new class of molecular sieves for molecular separation and electrochemical sensing based on the size of the molecules as well as interaction of the molecules with the surface functional groups of the tube. Normally, an inorganic nanotube membrane (polycarbonate or porous alumina) is set up to separate two salt solutions and a constant transmembrane potential is applied, then the transmembrane current is measured. When an analyte of comparable dimensions to the tube diameter is added to one of the solutions, a decrease in transmembrane current is sensed because of the current blocking by the molecules. Using such schemes, very small traces of different ions and molecules can be detected. These experiments, however, have all relied on using entire membranes as sensing elements. No significant efforts have been placed on single tube sensing, although the use of single nanotube sensing would obviously represent the miniaturization limit.
Nanofluidic channels and nanopores having dimensions comparable to the size of biological macromolecules such as proteins and DNA are important in applications such as single molecule detection, analysis, separation, and control of biomolecules. Previous work on nanopore or nanotube based single molecule detection can be broadly classified into two categories, namely: (i) non-functionalized nanopores; (ii) functionalized nanopores. Almost all of the prior work has involved the transmembrane protein ion channel α-Hemolysin (αHL) embedded in a suspended membrane separating two chambers filled with ionic solution. The entrance on the top (cis) side is about 2.6 nm in diameter whereas the narrow channel through the membrane that is closer to the bottom end (trans) is 1.4 nm in diameter. When a voltage bias of 120 mV is applied across the ion channel, an ionic current of about 120 pA is produced for ionic concentrations of 1 MKCl (the resistance is approximately 109Ω). However, biological nanopores such as α-hemolysin offer single molecule sensitivity but are labile and difficult to handle.
However, inorganic channels on solid state chips have advantages over organic channels including providing better control over channel geometry, increased mechanical, electrical, thermal and chemical stability and are more amenable to integration into functional systems.
Therefore, a need exists for nanofluidic devices and nanotube structures which can be readily implemented, such as within fluidic sensing applications. The present invention fulfills those needs and others, while overcoming the drawbacks inherent in prior nanodevice and nanostructure approaches.